Electrically-powered vehicles include hybrid vehicles and fully electric vehicles, such as battery electric vehicles (BEVs). Hybrid vehicles utilize a combination of an internal combustion engine and an electric motor, while fully electric vehicles utilize an electric motor. The electric motor may be mounted perpendicular to the vehicle axles, or it may be mounted transversely, that is, parallel to or coaxially with one or both vehicle axles.
A drive system of an electric vehicle may include an electric motor and a gearbox having one or more gear sets with a complex gear reduction system to achieve the desired output speed to each wheel. The electric motor and the gearbox may be housed within the same housing. However, providing hybrid or fully electric vehicles with gear reduction systems may present significant packaging problems because there is limited space in a vehicle to allow for a motor and a transmission whilst still allowing for adequate drive shaft lengths to prevent excessive angles on coupling joints during suspension articulation.
In addition, the housing for the electric motor and the gearbox may be formed from two or more housing units that are fastened together at joints. While effective, the joints between the housing units may suffer from sealing issues and provide a leakage path for oil. For example, the power electronic components mounted on the housing for operating the electric motor may exert pressure on the joints between the housing units and cause oil leakage, particularly when the power electronic components are large and heavy. Moreover, the fasteners used to couple the separate housing units may add to the overall weight of the drive system.
In addition to the aforementioned problems, electric vehicle drive systems that include compound (stepped) planetary gear sets may present further packaging issues. Stepped planetary gear sets may be favored by manufacturers due to their efficiency, but may require a relatively large radial packaging space due to a splined connection between the sun gear and external splines on the rotor shaft. That is, the sun gear in such systems may take up a significant amount of radial space to permit the splined connection.
Clearly, there is a need for improved electric vehicle drive system designs that reduce the packaging space and/or the weight of the drive system.